If, pursuant to the laws of Oklahoma or of any charter provision or ordinance of a city which participates in a city-county, county, district, or cooperative health department, as authorized by the Oklahoma Public Health Code, a retirement system is established for the employees of a participating city, the employees of the city-county, county, district, or cooperative health department may be included in that retirement system on the same basis applicable to employees of the participating city, provided the applicable board of health so recommends and the State Commissioner of Health, the board of county commissioners, and the governing body of the city which created and operates such health department approve. Nothing otherwise provided by law shall operate to prohibit the appropriation of county funds for the payment of the pro rata share of the contribution to be made to the city or county retirement fund on behalf of the employees of the applicable health department. In the event funds become available for public health purposes pursuant to the provisions of Section 9A, Article X of the Oklahoma Constitution and 63 O.S.Supp.1963, §§ 1-223 through 1-226, the contribution on behalf of the employees of the applicable health department may be paid from such funds; provided further, that an employee of the city-county, county, district, or cooperative health department shall not participate in more than one of the city, county, or state retirement systems.